AU771997B2

AU771997B2 - A method of amending database contents

Info

Publication number: AU771997B2
Application number: AU17920/01A
Authority: AU
Inventors: Richard H. Harvey
Original assignee: Computer Associates Think Inc
Current assignee: CA Inc
Priority date: 1999-11-26
Filing date: 2000-11-24
Publication date: 2004-04-08
Anticipated expiration: 2020-11-24
Also published as: AUPQ428599A0; CN1193307C; AU1792001A; EP1234255A1; JP2003515818A; WO2001039044A1; US7624096B1; IL149837A0; CN1399747A; EP1234255A4; CA2396444A1; ZA200203962B; BR0015914A; KR20020062309A

Description

WO 01/39044 PCT/US00/32121 A METHOD OF AMENDING DATABASE CONTENTS

BACKGROUND

1. Field The present application relates to the operational performance of a database, particularly its performance when the contents of the database are being altered. The present application has one, but not its only, application to a relational database, and more particularly a directory services database. In a further form, the invention relates to the performance of a database utilized in providing directory services. The invention, however, should not be limited to only this application.

2. Description of the Related Art A part of the problem which the present invention seeks to address, stems from a known situation in databases called "database isolation levels". Isolation levels allow a user to specify an appropriate compromise between consistency and concurrency. This feature makes it possible to increase concurrency when the consistency and accuracy of the data is not essential.

Many databases support four isolation levels as defined by the ANSI/ISO SQL92 standard. These levels are Read Uncommitted Read Committed Repeatable Read (RR) and Serializable.

The highest degree of isolation is called "Serializable", since the concurrent execution of serializable transactions is equivalent to a serial execution of the transactions. The Serializable level offers the highest degree of protection to the application programmer, high isolation. However, such high isolation often results in a lower degree of concurrency. At lower degrees of isolation, more transactions may run concurrently, but it can also introduce some inconsistencies in the data. The ANSI/ISO SQL92 standard identifies three inconsistencies that can occur during the execution of concurrent transaction: 1. "Dirty read": A transaction T1 modifies a row. A transaction T2 then reads that row before T1 performs a COMMIT. If T1 then performs a ROLLBACK, T2 will have read a row that was never committed and that may thus be considered to have never existed.

SUBSTITUTE SHEET (RULE 26) WO 01/39044 PCT/US00/32121 2. "Non-repeatable read": A transaction T1 reads a row. A transaction T2 then modifies or deletes that row and performs a COMMIT. If T1 then attempts to reread that row, it may receive the modified value or discover that the row has been deleted.

3. "Phantom rows": A transaction T1 reads a set of rows N that satisfy some <search condition>. A transaction T2 then executes SQL statements (or instructions) that generate one or more rows that satisfy the <search condition> used by transaction T1. If transaction T1 then repeats the initial read with the same <search condition>, it obtains a different collection of rows.

Table I below shows how the ANSI/ISO SQL92 standard defines which inconsistencies are possible (Yes) and which are not (No) for a given isolation level.

Dirty Non-repeatable Phantom Read Read rows READ UNCOMMITTED Yes Yes Yes READ COMMITTED No Yes Yes REPEATABLE READ No No Yes SERIALIZABLE No No No Table I Thus it can be seen that the "Serializable" level provides the highest isolation and the least possibility of inconsistencies, but, as noted above, this often results in the lowest level of performance. Conversely, the "read uncommitted" level which provides the lowest isolation and the highest possibility of inconsistencies, often results in the highest level of performance.

One reason isolation levels are an issue can be illustrated as follows.

When using a database, there may be one user wanting to update a row and another user wanting to read the same row. Depending on the isolation level selected, a database may lock a row when a row is being updated and thus the row cannot be read. This may not seem to be a major problem with only one user, but when there are many users, even thousands of users wanting to read a SUBSTITUTE SHEET (RULE 26) WO 01/39044 PCT/US0032121 database, such a 'lock' is found to be extremely wasteful of a users time. If the update takes a long time, this only exacerbates the problem of delaying the read by the other users.

One way around this problem is to allow reads and updates to go on concurrently, by selecting a lower isolation level. But this then leads to other problems. If the read is not locked during an update, the read function may be a "dirty read" on what is called a "dirty page" i.e. something may be read that is in the middle of being changed. To illustrate this problem, imagine in a payroll database, a first application is going through the database and increasing every payroll entry by 10%, while concurrently a second application is reading the database. If the first application had updated half the database entries and the second application had read all the database entries and had performed a sum operation to check the validity of the read, it would be found to be neither prevalue nor post-value. In essence, half the database had been updated by and the other half would not yet have been updated by 10% at the time the read operation occurred. So, in that particular instance, it may be considered more appropriate to run at a higher isolation level, but then again the performance or speed of a read will be reduced if the read is conducted at the higher isolation level.

In a directory services environment, which is usually a database I application that requires relatively high performance, the database I application deals with 'objects' and a metadata design. The directory system can be set at a relatively low isolation level in order to improve performance. But at the lower isolation levels, as illustrated above, the 'dirty read' problem can exist. The design of some directory systems utilize a table structure which includes, in effect, 'in' tables and 'out' tables. Figure 1 illustrates this.

The idea behind using an 'in' table and 'out' table structure, is that a search can be conducted on an 'in' table, a search table for example, and the results of that search can be based on an 'out' table, an entry table for example.

In Figure 1, lets say a search for Rick is called for. A search will find that Rick is SUBSTITUTE SHEET (RULE 26) Wn 9 I/o1tQAA Dd1lrfir Tcrbn/711 ItT 1 entry No. 123 and then the -result, from the entry table, is read from entry 123 together with the stored information associated with that entry.

Information in these tables may be included by adding rows to the search table, to the entry table and to other selected tables. The information may also S be stored in a raw form and/or a normalized form. However, if before the process of adding rows is completed, a read is performed not all the information that is being added to the entry table would be returned because not all the information had yet been added. This is what is referred to as a 'partial entry on add effect' and it manifests itself in that some (not all) of the added information may appear in results of a read. If this occurs, the read information is only partially correct.

Conversely, there is also what is called a 'partial entry on remove effect', where during a remove operation in which rows are being removed from tables, a search is performed before this removal operation is complete. The information returned from the search may not include information that has been deleted (or information that will be deleted very shortly after the search). Similarly there is what is called a 'partial entry on modify effect' which is in effect a combination of add and remove operations as outlined above, where either attributes of a particular entry in a database are added or removed.

What is described above, is an effect that can otherwise be referred to as an 'update' problem, or a partial entry problem. There is yet another problem in the prior art, in what may be called a partial entry replication problem. This partial entry replication problem stems from the situation where there are two independent systems that are being replicated using a database replication technique. In such a replication environment, it is desirable to replicate anything that happens on a 'master' database system on one or more 'slave' database systems. So when an entry which has been added, deleted or modified on the master database system it is desirable to also replicate any add, remove or modify operations on the slave database systems.

One reason this partial entry replication is considered a problem, is that an update may be fast on the 'master' database system, but is typically considerably slower when replicating on the slave database systems. Thus, instead of taking SUBSTITUTE SHEET (RULE 26) Dee 2003 9:41 SMOORENBURG ATTORNEYS +613 9712 0159 p.

4 milliseconds this replication may take seconds, depending on network traffic and the system configuration. With such delays, the partial entry replication problem can become quite noticeable to a user. Again, the problem is exacerbated if many updates are being done concurrently, which may be the case in a relatively large database.

Any discussion of documents, devices, acts or knowledge In this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art In Australia or elsewhere on or before the priority date of the disclosure and claims herein.

An object of the present invention Is to alleviate at least one disadvantage associated with the prior art.

SUMMARY

The present application provides, a method for improving the operational 15 performance of a database (or database system). In one embodiment, the method includes determining whether an Instruction or operation adds information to or removes information from the database. For an add operation, information is first added to an 'out' table used to retrieve objects (or entries) before the database is actually updated. For a remove operation, information is first 20 removed from an 'in' table used to find objects (or entries) in the database.

Preferably, for an add operation, the information is added to the 'in' table after the information is added to the 'out' table. Preferably, for a remove operation, information is removed from the 'out' table after the 'in' table.

The present invention also provides a method of replicating data from a 25 master database to a slave database, each database having Information organized in 'in' tables and 'out' tables, the method Including: updating the master database by determining whether an instruction or operation adds information or removes information from the database, wherein for an add operation, the information is first added to the 'out' table, and wherein for a remove operation, the information is first removed from the 'in' table, and updating the slave database in accordance with the same method as applied to the master database.

COMS ID No: SMBI-00523447 Received by IP Australia: Time 10:51 Date 2003-12-05 Dec 2003 9:41 SMOORENBURG RTTORNEYS +613 9712 0159 The present invention also provides a directory service arrangement including: a database using a plurality of tables, each table having a plurality of rows and columns, and storing arbitrary data, and means for processing an Instruction or operating by determining whether the instruction or operation adds information or removes information from the database, wherein for an add operation, the Information is first added to the 'out' table, and wherein for a remove operation, the information is first removed from the 'in' table.

The present invention also provides a directory service arrangement including: a master database using a plurality of tables, each table having a plurality of rows and columns, and storing arbitrary data, a slave database using a plurality of tables, each table having a plurality of 15 rows and columns, and storing arbitrary data, and Smeans for replicating between master and slave databases, wherein the master database Is updated by determining whether an Instruction or operation adds information or removes information from the database, wherein for an add operation, the information is first added to the 'out' table, and wherein for a 20 remove operation, the information is first removed from the 'in' table, and wherein the slave database is updated in accordance with the same method as applied to the master database.

Other aspects and preferred aspects are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the 25 invention.

According to an aspect of the present invention, when an add entry operation is performed, information is added to the entry table first, that Is to the 'out' table, such that the information is not visible initially. The information Is then added to the search table, that is the 'in' table, such that the information is visible and searchable so that all corresponding Information can be retrieved. Thus, according to this embodiment of the present application, Information to be added to a database is first prebuilt in a non-visible table before the information is made visible. As a result, If the information is searched prior to both 'in' and 'out' tables COMS ID No: SMBI-00523447 Received by IP Australia: Time 10:51 Date 2003-12-05 Dec 2003 9:41 SMOORENBURG ATTORNEYS +613 9712 0159 p.6 being completed, the 'in' table will not be active and the search returns a partially updated result. In other words, as rows are added to the 'in' table, the entry gradually becomes visible, and any search (on an 'in' table attribute) if found for a partially visible entry, the complete entry will be read.

The converse is true for a remove entry operation. For a remove entry operation information is removed from the 'in' table first and then the 'out' table.

Thus the visibility is first removed and then the contents are removed.

S COMS ID No: SMBI-00523447 Received by IP Australia: Time 10:51 Date 2003-12-05 WO 01/39044 PCTIUS00/32121 In an X.500 directory system, directory terms for services (or operations) are called add entry (for adding information), remove entry (for deleting information)., and modify entry (for modifying information).

In the instance of a replication operation, the present application forwards the replication information in the same order as entries are added, removed or modified, as described above. Thus if a master database system's 'in' table is first updated, this update may go into a replication queue so that the slave database system can be replicated in the same order as the master database system.

A Modify entry operation is a combination of add and remove. A modify entry operation is a collection of updates and is generally a sequence of changes, such as the addition of an attribute or value, or the removal of an attribute or value. So in the case of adding attributes or values, an "out" table/"in" table technique is used and when are removing attributes or values, the "in" table/"out" table technique is used. There may be zero or more add attribute, add value, remove attribute and or remove value operations in a modify entry operation.

BRIEF DESCRIPTION OF THE DRAWINGS The present embodiments will now be described with reference to the accompanying drawings in which: Figure 1 illustrates 'in' /'out' table structure, Figure 2 illustrates an add, remove or modify entry operation in schematic form in accordance with an embodiment of the present application, and Figure 3 illustrates a replication sequence in schematic form in accordance with the present invention.

DETAILED DESCRIPTION In order to help illustrate an embodiment of the present application, reference is made to the disclosure of PCT/AU95/00560 (US serial number 08/793,575 filed May 22, 1997), both of which are herein incorporated by reference, which provide a more detailed description of the 'add entry', 'remove entry' and 'modify entry' operations for an X.500 directory system. It should be SUBSTITUTE SHEET (RULE 26) WO 01/39044 PCT/US00/32121 noted, however, that the present application is not limited to the directory system disclosed in PCT/AU95/00560 (US serial number 08/793,575 filed May 22, 1997), and can be used in conjunction with any database system having an 'in' 'out' table design.

In order to exemplify the present embodiments, the X.500 directory system operations identified above will be used. However, it will also be appreciated that the subject matter of the .present application can be used in conjunction with other instructions (or operations) and database systems.

Add Entry Operation An Add Entry operation is used to add a leaf entry an object entry or an alias entry) to a Directory Information Tree (DIT). Table II below is an example of an X.500 Definition description.

Argument Description Object The Distinguished Name of the entry to be added Entry A set of attributes to add Common Arguments An optional set of controls to add Result Description NULL NULL Table II Generally, the steps of the Add Entry operation are as follows: Using the DIT table, tree walk to the parent of the entry to be added (Parent EID).

Using the DIT table, check if the entry exists check for RDN new RDN and PARENT Parent EID).

If the entry does not exist, allocate a new Entry Identifier (EID) and add the entry. Insert information into the DIT Table, the Name Table, the Tree Table, the Search Table, the Entry Table and, if it is an alias entry, the Alias Table.

An example of the process according to the present application for the SUBSTITUTE SHEET (RULE 26) Wfl IhI2O AA r-'T/I Mcnn 11 Add Entry operation is outlined below.

Example The objective of this example is to add an object with the following attributes and values under an object with a distinguished name (DN) of "Datacraft Marketing".

surname [Delahunty] commonName .[Mary] title [Marketing Manager] telephoneNumber 727-9523] To achieve this objective, first obtain the EID for the base object DN using a TreeWalk. The EID of the base object is "12".

Using the DIT Table, look for a duplicate entry, PARENT 12 and RDN "MARY DELAHUNTY". In this example, no duplicates exist.

Add the following rows to the tables shown.

DIT

EID PARENT ALIAS RDN 33 11 0 MARY DELAHUNTY

NAME

EID RAW 33 (Mary Delahunty]

TREE

EID PATH 33 1.12.21.

SEARCH

EID AID VID DISTING NORM 33 0 0 0 2.5.6.7 33 3 0 1 DELAHUNTY 33 4 0 1 MARY 33 12 0 0 MARKETING MANAGER 33 20 0 0 03 727 9523 SUBSTITUTE SHEET (RULE 26) WO 01/39044

ENTRY

PCT/US00/32121 EID AID VID RAW 33 0 0 [2.5.6.7] 33 3 0 [Delahunty] 33 4 0 [Mary] 33 12 0 [Marketing Manager] 33 20 0 727-9523] According to the present application, and referring to Figure 2, an instruction (step 21) would first be checked as to whether it added or removed information (step 22). In this case, it would add information, and thus information would be added to 'out' table first (step 23), and thereafter added to the 'in' table (step 24). It can be thus seen that for an 'add entry' operation, 'out' tables are added to first, then 'in' tables. Thus, with reference to the above example, information would be added to the ENTRY and NAME tables first (which are 'out' tables) and thereafter added to the SEARCH, DIT and TREE tables (which are 'in' tables).

Remove Entry Operation A Remove Entry operation is used to remove a leaf entry (either an object entry or an alias entry) from the Directory Information Tree (DIT). Table III below is an example of an X.500 Definition description.

Argument Description Object The Distinguished Name of the entry to be deleted Common Arguments An optional set of controls to add Result Description NULL NULL Table III Generally, the steps of the Remove Entry operation are as follows: S Perform a tree walk using the DIT table, to obtain the EID of the base object S If the entry exists, and it is a leaf entry, then for the condition EID EID of the selected object, delete information from the DIT Table, the Name Table, the Tree Table, the Search Table, the Entry Table and, if it is an alias entry, the Alias Table.

SUBSTITUTE SHEET (RULE 26) WO 01/39044 P('I I T A(I 121 An example of the process according to the present application for the Remove Entry operation is described below.

Example The objective of this example is to remove (or delete) an object with a distinguished name (DN) of "Datacraft Marketing Mary Delahunty." To achieve this object obtain the EID for the base object DN using a TreeWalk. The EID of the base object is Check that no entries have PARENT 21. Delete all rows added to the DIT Table, the Name Table, the Tree Table, the Search Table and the Entry Table (refer to Add Entry example above) where EID 21.

According to the present application, and referring again to Figure 2 an instruction (step 21) would first be checked as to whether it added or removed information (step 22). In this case, it would remove information, and thus information would be removed from the 'in' table first (step 25), and thereafter removed from the 'out' table (step 26). It can be thus seen that for a 'remove entry' operation, 'in' tables are removed from first, then 'out' tables. Thus, with reference to the above example, information would be deleted from SEARCH, DIT and TREE tables (which are 'in' tables) first and thereafter deleted from the ENTRY and NAME tables (which are 'out' tables).

Modify Entry Operation A Modify Entry operation is used to perform one or more of the following modifications to a single entry in the database. Table IV below is an example of an X.500 Definition description.

Argument Description Object The Distinguished Name of the entry to be modified Changes A list of modifications Common Arguments An optional set of-controls to add Result Description NULL

NULL

Table IV Generally, the steps of the Modify Entry operation are as follows: Perform a tree walk using the DIT table, to obtain the EID of the selected object.

SUBSTITUTE SHEET (RULE 26) unC nii nonAA V'rTn IcnnI 111 l V VA/OA^VA- T l.SI ,Af 711 t .fI For the selected object, perform one or more of the following actions: Add Value, Delete Value, Add Attribute, Delete Attribute in accordance with the method of the present application described above.

The operations required for each action are as follows: Add Value If the attribute exists, add the value to the Entry Table first, the "in" table, and thereafter the Search Table, the "out" table. A check is made to determine whether the attribute is single valued or multi-valued for an existing value. If the attribute is multi-valued a check for a duplicate value is then made. If a duplicate value is found, then the attribute value is not added.

Delete Value If the value exists, the value is deleted from the Search Table the "out" table) first, and thereafter deleted from the Entry Table the "in" table). Preferably, a Distinguished Name value is not deleted.

Add Attribute If the attribute does not exist, add the Attribute Values to the Entry Table the "in" table) first and thereafter to the Search Table the "out" table).

Delete Attribute For the Entry Table and the Search Table, if the attribute exists, delete it from the Search table first, and thereafter delete it from the Entry table.

Preferably, values with AID attr and EID base object are deleted, and Naming attributes are not deleted.

Example An example of the Modify operation is described below: The objective of this example is to modify the entry "Datacraft Sales Network Products Chris Masters" with the following changes: Delete Attribute and Value telephoneNumber 018 -042 671 Modify Attribute and Value title Sales Assistant SUBSTITUTE SHEET (RULE 26) WO 01/39044 PCT/US00/32121 The Search and Entry Tables below reflect the changes.

SEARCH

EID AID VID DISTING NORM 0 0 0 2.5.6.7 1 3 0 1 CHRIS 14 0 1 MASTERS 12 0 0 SALES ASSISTANT 20 0 0 03 727 9456

ENTRY

EID AID VID RAW 0 0 [2.5.6.71 3 0 [Chris] 4 0 [Masters) 12 0 [Sales Assistant] 20 0 727-9456] In accordance with one embodiment of the method of the present application, the Modify Entry operation would be performed as follows: adding a new attribute: add attribute to an 'out' table, such as the ENTRY table first, then add to 'in' tables, such as the SEARCH table. This would be accomplished in accordance with the sequence illustrated above with reference to Figure 2 relating to 'add entry'. The process as represented in Figure 2, would then determine if the instruction is a part of a 'modify' instruction (step 27), and as this is the case, would further determine if the instruction is complete (step 28), which at this stage it is not, and thus return to 22 for the next part of the sequence.

S removing an attribute remove an attribute from 'in' tables, such as the SEARCH table, first and then remove the attribute from the 'out' tables, such as ENTRY and NAME tables. Once the add or remove operations are completed, a determination is made of whether an instruction is part of a modify instruction (step 27) and if "yes" the process returns to step 22 to perform the next add or remove entry operation.

S adding attribute values add attribute values to an 'out' table, such as the ENTRY table, first and then add the attribute value to the 'in' tables, such as the SEARCH table. Once the attribute values are added, a SUBSTITUTE SHEET (RULE 26) Ul" l 0AnAl D"11"I Tenn 1111111 U/ f lu- Iv rf h.13 r UVIouua determination is made of whether an instruction is part of a modify instruction (step 27) and if "yes" the process returns to step 22 to perform the next add or remove entry operation.

removing attribute values remove attribute values from 'in' tables, such as the SEARCH table, first and then remove the attribute values from the 'out' tables, such as the ENTRY table. A determination is again made of whether an instruction is part of a modify instruction (step 27). At this stage, a 'no' determination is made and the process ends (steps 31 and 33 in Figure 3).

Some directory protocols define an attribute 'replace' operation. This can be performed by a sequence of a delete and an add operation. It is also to be noted that the present application has general application, and the embodiments described are illustrative only and not the only forms of implementing the present invention.

Database System Replication In the case of replication from master database system to one or more slave database systems, the present application calls for a sequence of operations, add entry, remove entry and/or modify entry, to be executed in the slave database systems in the same sequence as they were executed to update the master database system. Thus, referring to Figure 3, whether a replication procedure is required is determined at step 31, and if it is, the replication is executed (step 32) in accordance with the master database records, or records of the master database sequence (if not stored on the master database). Accordingly, the records of the master database sequence of operations is obtained or accessed and the replication is performed. This information is passed on to the slave database systems and executed in the slave database systems during a replication procedure. At the end of the replication sequence, the procedure ends (step 33).

While there are a number of examples given in this specification, it is to be noted that the system and method of the present application should not be limited to only those operations as exemplified. The present application can be SUBSTITUTE SHEET (RULE 26) Dec 2003 9:41 SMOORENBURG ATTORNEYS +613 9712 0159 p.

7 14 applied to numerous operations or instructions based on the out/in or in/out technique as disclosed above.

Equally, the present application, although described in relation to a table structure as disclosed in PCT/AU95/00560 (US serial Number 08/793,575 filed May 22, 1997) is equally applicable to any type of table structure that separates 'in' (searchable attributes) from 'out' (Information that can be retrieved). The present invention relates to the method/apparatus used to execute Instructions or operations, or the structure upon which the operations or Instructions are executed.

"Comprises/comprising" when used In this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, Integers, steps, components or groups thereof.

V.

0 COMS ID No: SMBI-00523447 Received by IP Australia: Time 10:51 Date 2003-12-05

Claims

1. A method for improving the operational performance of a database system, the method including: determining whether an instruction or operation adds information or removes information from the database system, wherein for an add operation, the information is first added to an 'out' table and wherein for a remove operation, the information Is first removed from an 'in' table.

2. A method as claimed In Claim 1, wherein the Information is added to the 'in' table after being added to the 'out' table.

3. A method as claimed in Claim 1, wherein the information is removed from the 'out' table after being removed from the 'in' table. s

4. A method as claimed In Claim 1. further including determining whether the instruction modifies Information, and if so, performing both the add and remove operations. 20

5. A method as claimed in Claim 1, wherein the instructions are implemented via a directory system such X.500 or LDAP. .i S

6. A method of replicating data from a master database to a slave database, each database having information organized in 'in' tables and 'out' tables, the 25 method including: updating the master database by determining whether an instruction or operation adds Information or removes information from the database, wherein for an add operation, the information is first added to the 'out' table, and wherein for a remove operation, the information is first removed from the 'in' table, and updating the slave database in accordance with the same method as applied to the master database. COMS ID No: SMBI-00523447 Received by IP Australia: Time 10:51 Date 2003-12-05 17 Feb 2004 20:07 Smoorenburg Attorneyss +613 9712 0159 p.4 16

7. A method as claimed In Claim 6, wherein an updating process as applied to the master database is placed in a replication queue prior to being passed onto the slave database.

8. A method as claimed in Claim 6, wherein Information updated in the master database is placed in a replication queue prior to being passed onto the slave database.

9. A method as claimed in Claim 6, wherein the slave database is updated in the same sequence of instructions or operations as the master database.

10. A method as claimed in Claim 6, wherein the instructions are implemented via a directory system such as X.500 or LDAP. 15

11. A directory service arrangement including: a database using a plurality of tables, each table having a plurality of rows and columns, and storing arbitrary data, and means for processing an instruction or operation by determining whether the instruction or operation adds information or removes information from the 20 database, wherein for an add operation, the information is first added to the 'out' table, and wherein for a remove operation, the information is first removed from the 'in' table.

12. An arrangement as claimed in Claim 11, being a directory services system such as X.500 or LDAP.

13. A directory service arrangement including: a master database using a plurality of tables, each table having a plurality of rows and columns, and storing arbitrary data, a slave database using a plurality of tables, each table having a plurality of rows and columns, and storing arbitrary data, and COMS ID No: SMBI-00623209 Received by IP Australia: Time 20:09 Date 2004-02-17 Dec 2003 9:42 SMOORENBURG ATTORNEYS +613 9712 0159 p. 1 0 17 means for replicating between master and slave databases, wherein the master database is updated by determining whether an instruction or operation adds information or removes information from the database, wherein for an add operation, the information Is first added to the 'out' table, and wherein for a remove operation, the information Is first removed from the 'In' table, and wherein the slave database is updated in accordance with the same method as applied to the master database.

14. An arrangement as claimed in Claim 13, being a directory services system such as X.500 or LDAP. A method as claimed In Claim 1 or 6, substantially as herein described with reference to the accompanying drawings.

15

16. An arrangement as claimed in Claim 11 or 13, substantially as herein described with reference to the accompanying drawings. DATED this 5th day of December 2003 COMPUTER ASSOCIATES THINK INC SMOORENBURG PATENT TRADE MARK ATTORNEYS S: PO BOX 9 KANGAROO GROUND VIC 3097 AUSTRALIA COMS ID No: SMBI-00523447 Received by IP Australia: Time 10:51 Date 2003-12-05